I personally would be quite concerned. However, I suppose one needs to ask some basic questions in order to ascertain whether it is poor admin or a con.
First off, was the seller a legitimate exhibitor/seller? Did they have an official stand etc or was the deal done elsewhere eg in a carpark, cafe etc?
What paperwork did your mate receive there and then eg a receipt and what was specified on it? Does it look official and does the company name and individual seller's name appear on it? You can then make checks ref.whether this company is legit and whether the seller is an employee of them etc.
If the answers so far aren't promising, you could also contact the shooting show organisers/admin team to establish what they know of the seller etc
If looks like it's a legitimate/genuine company, it could just be a mess up or very inefficient employee. A telephone call to the manager/owner might be required to get things moving.
If it ends looking like a con, then your mate could explore options of trying to get his money back from the card company if he paid by credit card etc.
.....
Hopefully this will have a happy ending.
It did get me thinking of some of the old con tricks out there. I remember when a builder friend was doing some work for me when a van stopped outside and the guy told the builder he had just finished at a sales exhibition and he had some Makita tools that he wanted to get rid of and hence could do them at a knock down price. My mate bought a drill but later confided in me that what it was clearly a knock off/counterfeit one.